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Defer resolution of a recursion variable during union unification until merging
While unifying two unions, we may turn one of them into a recursive union. If we don't recognize the recursiveness before merging, we'll have lost the recursive value of the union.
This commit is contained in:
Ayaz Hafiz
parent
5ec2715820
commit
238e64c0b3
2 changed files with 40 additions and 40 deletions
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@ -2721,7 +2721,6 @@ fn unify_tag_unions<M: MetaCollector>(
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initial_ext1: TagExt,
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tags2: UnionTags,
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initial_ext2: TagExt,
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recursion_var: Rec,
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) -> Outcome<M> {
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let (separate, mut ext1, mut ext2) =
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separate_union_tags(env.subs, tags1, initial_ext1, tags2, initial_ext2);
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@ -2781,7 +2780,6 @@ fn unify_tag_unions<M: MetaCollector>(
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shared_tags,
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OtherTags2::Empty,
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merge_tag_exts(ext1, ext2),
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recursion_var,
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);
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shared_tags_outcome.union(ext_outcome);
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@ -2818,15 +2816,8 @@ fn unify_tag_unions<M: MetaCollector>(
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let combined_ext = ext1.map(|_| extra_tags_in_2);
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let mut shared_tags_outcome = unify_shared_tags(
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env,
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pool,
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ctx,
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shared_tags,
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OtherTags2::Empty,
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combined_ext,
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recursion_var,
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);
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let mut shared_tags_outcome =
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unify_shared_tags(env, pool, ctx, shared_tags, OtherTags2::Empty, combined_ext);
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shared_tags_outcome.union(ext_outcome);
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@ -2881,15 +2872,8 @@ fn unify_tag_unions<M: MetaCollector>(
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let combined_ext = ext2.map(|_| extra_tags_in_1);
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let shared_tags_outcome = unify_shared_tags(
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env,
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pool,
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ctx,
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shared_tags,
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OtherTags2::Empty,
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combined_ext,
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recursion_var,
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);
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let shared_tags_outcome =
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unify_shared_tags(env, pool, ctx, shared_tags, OtherTags2::Empty, combined_ext);
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total_outcome.union(shared_tags_outcome);
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if extend_ext_with_uninhabited {
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@ -2954,8 +2938,7 @@ fn unify_tag_unions<M: MetaCollector>(
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env.subs.commit_snapshot(snapshot);
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let shared_tags_outcome =
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unify_shared_tags(env, pool, ctx, shared_tags, other_tags, ext, recursion_var);
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let shared_tags_outcome = unify_shared_tags(env, pool, ctx, shared_tags, other_tags, ext);
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total_outcome.union(shared_tags_outcome);
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total_outcome
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}
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@ -3075,6 +3058,24 @@ fn choose_merged_var(subs: &Subs, var1: Variable, var2: Variable) -> Variable {
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}
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}
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#[inline]
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fn find_union_rec(subs: &Subs, ctx: &Context) -> Rec {
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match (
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subs.get_content_without_compacting(ctx.first),
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subs.get_content_without_compacting(ctx.second),
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) {
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(Structure(s1), Structure(s2)) => match (s1, s2) {
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(FlatType::RecursiveTagUnion(l, _, _), FlatType::RecursiveTagUnion(r, _, _)) => {
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Rec::Both(*l, *r)
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}
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(FlatType::RecursiveTagUnion(l, _, _), _) => Rec::Left(*l),
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(_, FlatType::RecursiveTagUnion(r, _, _)) => Rec::Right(*r),
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_ => Rec::None,
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},
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_ => Rec::None,
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}
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}
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#[must_use]
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fn unify_shared_tags<M: MetaCollector>(
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env: &mut Env,
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@ -3083,7 +3084,6 @@ fn unify_shared_tags<M: MetaCollector>(
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shared_tags: Vec<(TagName, (VariableSubsSlice, VariableSubsSlice))>,
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other_tags: OtherTags2,
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ext: TagExt,
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recursion_var: Rec,
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) -> Outcome<M> {
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let mut matching_tags = Vec::default();
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let num_shared_tags = shared_tags.len();
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@ -3192,6 +3192,13 @@ fn unify_shared_tags<M: MetaCollector>(
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}
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};
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// Look up if either unions are recursive, and if so, what the recursive variable is.
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//
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// We wait until we're about to merge the unions to do this, since above, while unifying
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// payloads, we may have promoted a non-recursive union involved in this unification to
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// a recursive one.
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let recursion_var = find_union_rec(env.subs, ctx);
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let merge_outcome = unify_shared_tags_merge(env, ctx, new_tags, new_ext_var, recursion_var);
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total_outcome.union(merge_outcome);
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@ -3275,24 +3282,20 @@ fn unify_flat_type<M: MetaCollector>(
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}
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(TagUnion(tags1, ext1), TagUnion(tags2, ext2)) => {
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unify_tag_unions(env, pool, ctx, *tags1, *ext1, *tags2, *ext2, Rec::None)
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unify_tag_unions(env, pool, ctx, *tags1, *ext1, *tags2, *ext2)
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}
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(RecursiveTagUnion(recursion_var, tags1, ext1), TagUnion(tags2, ext2)) => {
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debug_assert!(is_recursion_var(env.subs, *recursion_var));
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// this never happens in type-correct programs, but may happen if there is a type error
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let rec = Rec::Left(*recursion_var);
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unify_tag_unions(env, pool, ctx, *tags1, *ext1, *tags2, *ext2, rec)
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unify_tag_unions(env, pool, ctx, *tags1, *ext1, *tags2, *ext2)
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}
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(TagUnion(tags1, ext1), RecursiveTagUnion(recursion_var, tags2, ext2)) => {
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debug_assert!(is_recursion_var(env.subs, *recursion_var));
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let rec = Rec::Right(*recursion_var);
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unify_tag_unions(env, pool, ctx, *tags1, *ext1, *tags2, *ext2, rec)
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unify_tag_unions(env, pool, ctx, *tags1, *ext1, *tags2, *ext2)
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}
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(RecursiveTagUnion(rec1, tags1, ext1), RecursiveTagUnion(rec2, tags2, ext2)) => {
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@ -3307,8 +3310,7 @@ fn unify_flat_type<M: MetaCollector>(
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env.subs.dbg(*rec2)
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);
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let rec = Rec::Both(*rec1, *rec2);
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let mut outcome = unify_tag_unions(env, pool, ctx, *tags1, *ext1, *tags2, *ext2, rec);
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let mut outcome = unify_tag_unions(env, pool, ctx, *tags1, *ext1, *tags2, *ext2);
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outcome.union(unify_pool(env, pool, *rec1, *rec2, ctx.mode));
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outcome
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@ -3407,7 +3409,7 @@ fn unify_flat_type<M: MetaCollector>(
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);
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let tags2 = UnionTags::from_slices(*tag_names, empty_tag_var_slices);
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unify_tag_unions(env, pool, ctx, *tags1, *ext1, tags2, *ext2, Rec::None)
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unify_tag_unions(env, pool, ctx, *tags1, *ext1, tags2, *ext2)
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}
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(FunctionOrTagUnion(tag_names, _, ext1), TagUnion(tags2, ext2)) => {
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let empty_tag_var_slices = SubsSlice::extend_new(
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@ -3416,7 +3418,7 @@ fn unify_flat_type<M: MetaCollector>(
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);
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let tags1 = UnionTags::from_slices(*tag_names, empty_tag_var_slices);
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unify_tag_unions(env, pool, ctx, tags1, *ext1, *tags2, *ext2, Rec::None)
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unify_tag_unions(env, pool, ctx, tags1, *ext1, *tags2, *ext2)
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}
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(RecursiveTagUnion(recursion_var, tags1, ext1), FunctionOrTagUnion(tag_names, _, ext2)) => {
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@ -3428,9 +3430,8 @@ fn unify_flat_type<M: MetaCollector>(
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std::iter::repeat(Default::default()).take(tag_names.len()),
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);
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let tags2 = UnionTags::from_slices(*tag_names, empty_tag_var_slices);
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let rec = Rec::Left(*recursion_var);
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unify_tag_unions(env, pool, ctx, *tags1, *ext1, tags2, *ext2, rec)
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unify_tag_unions(env, pool, ctx, *tags1, *ext1, tags2, *ext2)
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}
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(FunctionOrTagUnion(tag_names, _, ext1), RecursiveTagUnion(recursion_var, tags2, ext2)) => {
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@ -3441,9 +3442,8 @@ fn unify_flat_type<M: MetaCollector>(
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std::iter::repeat(Default::default()).take(tag_names.len()),
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);
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let tags1 = UnionTags::from_slices(*tag_names, empty_tag_var_slices);
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let rec = Rec::Right(*recursion_var);
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unify_tag_unions(env, pool, ctx, tags1, *ext1, *tags2, *ext2, rec)
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unify_tag_unions(env, pool, ctx, tags1, *ext1, *tags2, *ext2)
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}
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// these have underscores because they're unused in --release builds
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